1. Technical Field
The invention relates to a source driver and a method for reducing peak current in the source driver.
2. Related Art
FIG. 1 is a circuit block schematic diagram of a conventional source driver (SD) 100. The source driver 100 is coupled between a timing controller 10 and a display panel 20. A power supply voltage VDDA can be supplied to the source driver 100. Under control of the timing controller 10, the source driver 100 can convert pixel data provided by the timing controller 10 into driving voltages, and drive the display panel 20 by using the driving voltages to display a corresponding image. The source driver 100 includes a data receiver 110, a latch 120, a digital-to-analog converter (DAC) 130 and an output buffer 140.
FIG. 2 is a signal timing schematic diagram of the source driver 100 of FIG. 1. Referring to FIG. 1 and FIG. 2, the latch 120 receives pixel data transmitted from the timing controller 10 through the data receiver 110, and latches the pixel data in corresponding channels. According to a timing of a latch signal LD, the latch 120 can output pixel data D1, D2, D3, . . . , Dx−1 and Dx latched in different channels to the DAC 130. The DAC 130 respectively converts the pixel data D1−Dx in different channels into corresponding analog grayscale voltages I1, I2, I3, Ix−1 and Ix according to a GAMMA voltage VG. The output buffer 140 respectively outputs corresponding driving voltages to different data lines Y1, Y2, Y3, . . . , Yx−1 and Yx of the display panel 20 according to the analog grayscale voltages I1-Ix in different channels.
As that shown in FIG. 2, since the latch 120 updates the new pixel data to an input terminal of the DAC 130 according to a rising time point of the latch signal LD in a parallel manner, when the new pixel data is a complement of the old pixel data, a power supply current I(VDDA) of the source driver 100 may produce a large instantaneous peak current. As that shown in FIG. 2, when the new (current) pixel data (for example, FF) is the complement of the old (previous) pixel data (for example, 00), the power supply current I(VDDS) of the source driver 100 may produce an instantaneous peak current shown by a dot line circle 200 in FIG. 2. The instantaneous peak current generally causes instantaneous drop of the voltage level of the power supply voltage VDDA, which influences a normal operation of the internal circuit. Besides, instantaneous drop of the voltage level of the power supply voltage VDDA also has an electromagnetic interference (EMI) effect on the system.